[NTP Snippets] Persist snippets in a LevelDB instead of prefs

components/ntp_snippets/ntp_snippets_constants.h

Index: components/ntp_snippets/ntp_snippets_constants.h
diff --git a/components/ntp_snippets/ntp_snippets_constants.h b/components/ntp_snippets/ntp_snippets_constants.h
index c12ce9360abea628178cf9bb442b5122480c6d49..0bb403cba5d03de168218b3f5c02f8afb68a3a52 100644
--- a/components/ntp_snippets/ntp_snippets_constants.h
+++ b/components/ntp_snippets/ntp_snippets_constants.h
@@ -5,11 +5,18 @@
 #ifndef COMPONENTS_NTP_SNIPPETS_CONSTANTS_H_
 #define COMPONENTS_NTP_SNIPPETS_CONSTANTS_H_
 
+#include "base/files/file_path.h"
+
 namespace ntp_snippets {
 
 // Name of the variation parameters study to configure NTP snippets.
 extern const char kStudyName[];
 
+// Name of the folder where the snippets database should be stored. This is only
+// the name of the folder, not a full path - it must be appended to e.g. the
+// profile path.
+extern const base::FilePath::CharType kDatabaseFolder[];
+
 }  // namespace ntp_snippets
 
 #endif